Many touch-capable web browsers allow the user to zoom webpages utilizing a gesture, such as a pinch gesture. Typically, the zoom functionality is implemented as an optical stretch of the page, referred to as an “optical zoom.” By definition, this conflicts with W3C standards which require the page to re-layout based on the visible region.
Many web browsers basically just ignore this standards requirement. This, in turn, implies that other features stop working or can work differently than expected. These include fixed-position elements and backgrounds, (Document Object Model) DOM values reported in script, and other aspects of page layout. This results in compatibility issues with websites which use these features, often to the extent that the sites are forced to create special versions for certain browsers or devices to avoid broken functionality.